1. Technical Field
This invention relates to a process and an apparatus for mixing a fluid or a liquid within a vessel or a tank.
2. Discussion of Related Art
The recent trend of higher prices in crude oils and the availability of supply necessitates that refineries have the abilities to process various different types of crude oils, while providing consistent and safe operations of the process units. One way that refineries seek to capture economic benefits of crude feedstock flexibility is by blending various feedstocks before processing in the crude oil distillation unit or pipe still, such as blending a less expensive heavy crude oil with a lighter crude oil. A typical manner to blend the crude oil materials is in the crude oil storage tanks. The crude oil storage tanks hold large volumes, such as up to about 125,000 meters cubed.
Known devices for mixing crude oil tanks include side entry agitators with marine type propellers. These agitators do not satisfactorily mix the two or more crude oils and significant operational and safety issues arise as the unmixed crude is supplied to the refinery. Recent publications in scientific journals disclose using computational fluid dynamics to model crude oil tank mixing with agitators and/or combining the agitator with a jet mixer.
Cheremisinoff in the “Handbook of chemical process equipment” states for blending to practical homogeneity, ten tank turnovers are recommended and for blending to an approximate 1 percent deviation between top and bottom sample points in a tank, three tank turnovers are normally adequate. Similarly, Paul in “Handbook of industrial mixing: science and practice” states for a liquid with a viscosity of less than 100 centipoise 3 turnovers are needed to reach 95 percent homogeneity in a tank, and for a viscosity of 100 centipoise to less than 1000 centipoise 10 turnovers are needed to reach 95 percent homogeneity in a tank.
Atwood, U.S. Pat. No. 2,322,087, discloses an eductor tank mixer where the entrained fluid is drawn simultaneously from all levels of fluid within the tank. The orifices of the intake mixing tube are proportioned that the amount drawn from each level increases upwardly along the intake mixing tube.
Kuerten et al., U.S. Pat. No. 3,847,375, discloses a method of mixing liquids which differ greatly from one another as regards their volume and/or density. The liquid dispersing agent is passed into in impulse exchange chamber.
Colebrander, International Publication Number WO01/03816, discloses a method of introducing a first liquid in a stirred vessel containing a second liquid by injecting the first liquid into the stirred vessel, wherein a ratio of injection velocity over impeller tip speed is greater than 2.
Although the foregoing disclosures provide advances in the art, there is still a need and a desire to rapidly mix and/or homogenize a contents of a vessel. There is also a need and a desire to mix a first liquid stratified on a second to make a uniform feed to a process unit. Furthermore, there is a need and a desire to mix liquids with density and/or viscosity differences.